Method for producing a continuous casting mold and a continuous casting mold produced by this method

ABSTRACT

A continuous casting mold having at least one mechanically machined surface that is in contact with molten material during normal use of the mold in order to achieve a uniform distribution of the heat flux over the mold.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional Application of U.S. patentapplication Ser. No. 11/885,808, filed Sep. 6, 2007, which is a 371 ofInternational application PCT/EP2006/002164, filed Mar. 9, 2006, whichclaims priority of DE 10 2005 011 532.2, filed Mar. 10, 2005, and DE 102005 023 745.2, filed May 24, 2005, the priority of these applicationsis hereby claimed and these applications are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a method for producing a continuous casting mold,in which machining is carried out on at least one surface which is incontact with molten material during the normal use of the mold. Theinvention also concerns a continuous casting mold.

2. Description of the Related Art

Continuous casting molds are known which are characterized by a specialsurface modification, especially for the purpose of favorably affectingheat transfer from the steel into the mold wall.

EP 1 099 496 A1 proposes that mold plates be completely or partiallyprovided with surface texture to reduce heat flow. The texture ispreferably produced by sand blasting or shot peening after machining.This makes it possible to increase the roughness of the surface of themold that is in contact with molten material during normal use of thecontinuous casting mold.

JP 10 193 042 A describes a continuous casting mold in whichlongitudinal grooves are systematically formed in the surface of thebroad-side plates. This is intended to reduce the heat flux density inthe liquid metal level in order to avoid longitudinal cracks.

JP 02 020 645 A discloses a continuous casting mold in whichlongitudinal grooves and transverse grooves are formed in the broad-sideplates in a predetermined grid pattern. The goal here is also to reducethe heat flux density in the liquid metal level and thus to reduce therisk of longitudinal cracks.

The grooves that are formed are in the range of 0.5 to 1.0 mm; the gridspacing is about 5-10 mm.

AT 269 392 discloses a continuous casting mold in which the goal islikewise to reduce the heat flux density, especially in the upper partof the mold. This is achieved by a greater wall thickness in the upperpart of the mold or by the use of more strongly insulating material inthis area. In this regard, the upper area of the mold either can consistentirely of this material or can be coated with this material on thewater side.

FR 2 658 440 describes a continuous casting mold in which localreduction of the heat flux density is realized by forming grooves in thehot side of the mold and filling these grooves with a second material oflower thermal conductivity. In addition, the entire surface of the moldis coated with this second material.

JP 06 134 553 A and JP 03 128 149 A describe roughening the surface ofcasting rolls, which is intended in this application to reduce the heatflux density.

SUMMARY OF THE INVENTION

The previously known measures are intended to bring about improvedthermodynamic behavior of the mold and especially its walls and improvedsuitability for use in continuous casting. In general, one strives forgood adhesion of the casting flux to the mold plate and uniformdistribution of the heat flow over the entire mold.

The thickness and the structure of the casting flux layer between themold wall and the strand shell are critical determinants of themagnitude of the heat flux density between the steel and the mold andthus of the thermal load on both the strand shell and the mold material.Therefore, strong stresses can arise in the strand shell due to localchanges and changes over time in the casting flux layer, and thesestresses can cause longitudinal cracks, especially in steel grades thatare susceptible to cracking. However, the surface of the mold is alsosubject to strong mechanical stresses due to alternating thermalloading. Therefore, the maximum heat flow in the area of the liquidmetal level should be low and as uniform as possible in order to reducethe risk of cracking, especially in steel grades that are susceptible tolongitudinal cracking.

An additional goal is to keep the friction between the broad sides andthe narrow sides of the mold as low as possible during adjustment of thenarrow sides. Finally, it is desirable to reduce the thermal stress inthe liquid metal level by means of a low heat flux density for thepurpose of increasing the service life of the mold.

The measures that have previously been proposed achieve these goals onlypartially or at relatively high production expense.

Therefore, the goal of the invention is to develop a continuous castingmold and a method for producing it, with which the aforementioneddesired characteristics can be achieved as effectively as possible, withthe least possible production expense, and thus at low cost.

In accordance with the invention, the solution to this problem withrespect to a method is characterized by the fact that machining thatproduces an anisotropically textured surface is carried out as the lastprocessing step or as one of the last processing steps in the productionof the surface of the mold.

This is preferably accomplished by employing a milling process or agrinding process as the last processing step.

Anisotropy is understood to mean that the surface characteristics varywith the surface direction in which they are determined. In connectionwith the mold surface in question here, this means especially thatvarious parameters, such as roughness, have different values whenmeasured in the casting direction from their values perpendicular to thecasting direction, i.e., in the direction transverse to the castingdirection.

In accordance with the invention, the continuous casting mold, which hasat least one machined surface that has contact with molten materialduring its normal use, is characterized by the fact that at least partof the surface has an anisotropic structure.

In one embodiment of the invention, the surface of the mold has greaterroughness in the casting direction than in the direction transverse tothe casting direction, in each case as viewed in the plane of thesurface.

The anisotropically textured surface can have elevations and depressionsformed and oriented in rows that run in the direction transverse to thecasting direction. The elevations and depressions can be formed ascorrugations, whose peaks and valleys run in the direction transverse tothe casting direction; in this connection, the corrugations preferablyhave an essentially rounded shape in cross section. It has been found tobe effective if the height of the corrugations is 2 μm to 250 μm, andespecially 10 μm to 50 μm.

The height of the corrugations on the surface can remain constant or canbe varied in the casting direction and/or in the direction transverse tothe casting direction.

The proposal of the invention is thus aimed at producing the desiredanisotropic surface structure in the last step of the machiningoperation to shape the surface of the mold. In this regard, the machinedsurface can be shaped in such a way that the macroscopic structureproduced in the casting direction is different from that producedtransverse to the casting direction. The microscopic roughness of thesurface can also be formed differently in the casting direction and thedirection transverse to the casting direction.

Greater roughness in the casting direction and a macroscopic structureof the surface with elevations running in rows transverse to the castingdirection result in better adhesion of the casting flux layer to themold plate near the liquid metal level, so that it is not so easilyrubbed off—completely or only locally—by the strand. At the same time,both the increased roughness and the macroscopic structure of thesurface cause the heat flow to be reduced and evened out, which alsoresults in a reduction of the tendency towards longitudinal cracking. Inaddition, the reduction of the heat flux density in the liquid metallevel reduces the thermal stresses in the mold plate, which increasesthe service life of the mold plates.

Furthermore, it is advantageous that the desired surface texture isproduced during the machining of the mold surface. This means thatfurther processing steps, e.g., forming grooves in the surface, coatingthe surface in the area of the liquid metal level, or roughening thesurface by sand blasting or shot peening, are not necessary, which makesthe proposal of the invention economical. The advantageous anisotropicsurface texture can thus be produced without great expense not onlyduring the production of the molds but also during each reworking of themold surface, which is necessary at certain intervals of time.

In addition, the shaping of the mold surfaces in the manner describedwith macroscopic elevations oriented transversely to the castingdirection, or the roughness that is greater in the casting directionthan in the direction transverse to the casting direction, also reducesthe friction between the broad sides and the narrow sides duringadjustment of the narrow sides in the case of molds that consist ofindividual mold plates (e.g., slab, thin slab).

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 shows a schematic representation of a mold plate with ananisotropic surface and an enlarged view of the surface topology.

FIG. 2 shows a schematic three-dimensional view of the profile of thesurface of the mold plate.

FIG. 3 shows an enlarged view of section A-B in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a view of that surface of a mold plate of a continuouscasting mold 1 which is in contact with molten material (steel) or thesolidified strand shell during the use of the continuous casting mold 1.The strand shell passes the mold plate in casting direction G. Toachieve the advantages explained above, the surface 2 is provided with aspecial texture: The surface topology, especially the roughness, of thesurface 2 is anisotropically formed, i.e., different roughness valuesare measured in casting direction G and in direction Q transverse to thecasting direction G.

In this connection, the mold plate is provided with large numbers ofelevations and depressions, which are shown in FIG. 1 in a highlyschematic way. These elevations and depressions are produced during thelast machining operation in the production of the mold plate. In thelast machining step, the surface of the mold plate is milled by traversemilling, for example, with the use of a milling cutter with a diameterof 100-150 mm, which is provided with standard indexable cutter inserts,e.g., made of cemented carbide alloy. The material removal during thelast machining step is less than 1 mm, and preferably less than 0.5 mm.Impressions and the structure of the elevations and depressions on thesurface of the mold can be systematically adjusted according to theselected material removal and other milling parameters, such as speed ofrotation, feed rate, peripheral speed, spacing of the milled rows,coolant, milling direction, and angle of attack of the tool relative tothe surface of the plate (set angle).

Alternatively, the desired surface texture can be produced by a grindingprocess. As in the case of milling, the surface can be ground in rows.In this regard, the shape of the wavelike elevations and depressions canbe produced by the surface contour of the grinding disk or by the angleof attack of the grinding disk relative to the surface of the plate.

FIG. 2 shows a three-dimensional view of the profile of the surfaceafter the final machining. Here it is apparent that the roughness of thesurface is greater in the casting direction G than in the direction Qtransverse to the casting direction G. The mold plate is thus providedwith a large number of elevations and depressions, which are shown onlyin a highly schematic way in FIG. 1. These elevations and depressionsare produced during the last machining operation in the production ofthe mold plate.

The height H of the elevations and depressions, which are oriented inrows, is seen in FIG. 3 and is typically in the range of 2 μm to 250 μm,which can be controlled by the choice of milling parameters.

1. A continuous casting mold having at least one machined surface thatis contactable with molten material during normal use, wherein at leastpart of the surface has an anisotropic structure so that the surface hasa roughness with different values when measured in a casting directionthan values when measured in a direction transverse to the castingdirection.
 2. The continuous casting mold in accordance with claim 1,wherein the surface has greater roughness in the casting direction thanin the direction transverse to the casting direction.
 3. The continuouscasting mold in accordance with claim 1, wherein the surface haselevations and depressions formed and oriented in rows that run in thedirection transverse to the casting direction.
 4. The continuous castingmold in accordance with claim 3, wherein the elevations and depressionsare formed as corrugations with peaks and valleys that run in thedirection transverse to the casting direction.
 5. The continuous castingmold in accordance with claim 4, wherein the corrugations have anessentially rounded shape in cross section.
 6. The continuous castingmold in accordance with claim 4, wherein the corrugations have a heightof 2 μm to 250 μm,
 7. The continuous casting mold in accordance withclaim 6, wherein the corrugations have a height of 10 μm to 50 μm. 8.The continuous casting mold in accordance with claim 4, wherein thecorrugations have a uniform height in the casting direction.
 9. Thecontinuous casting mold in accordance with claim 4, wherein thecorrugations have a varying height in the casting direction.